Matrix to Quaternion conversion precision fix.

See below links for reasoning, but in short, avoid sqrt and division
of small values. It's also possible to normalize the quaternion after
the conversion, but better precision is preferable.

http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/index.htm
http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/ethan.htm
ColladaParser: Tolerate empty data arrays and controller weights.
fixed sample.py
Fixed pyassimp core.py
Merge github.com:rodrigob/assimp
Fixing compilation on gcc 4.5.2
Merge git://github.com/assimp/assimp
update : add displacement map support to obj-material importer. this feature is supported by some special exporters.

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@1347 67173fc5-114c-0410-ac8e-9d2fd5bffc1f
Merge pull request #13 from rodrigob/master

Fixes to pyassimp
Merge pull request #12 from ccxvii/master

Precision fix and Collada robustness fix.
Merge branch 'master' of git://github.com/assimp/assimp
Revert "- update readme to describe my fbx work and to link to blenderwiki."

This reverts commit bd98ee86817f1d111f92adf8b177bde1b24a20ba.
- some fixes for vc12
- more vc12 fixes